Laudator Temporis Acti

Matthew 12.1-2 (par. Mark 2.23-24 and Luke 6.1-2):

At that time Jesus went on the sabbath day through the corn; and his disciples were an hungred, and began to pluck the ears of corn, and to eat. But when the Pharisees saw it, they said unto him, Behold, thy disciples do that which is not lawful to do upon the sabbath day.

We are not told who owned the corn and what he thought about it. The Pharisees accuse the disciples of violating the fourth commandment (Exodus 20.8, Remember the sabbath day, to keep it holy), not the eighth (Exodus 20.15, Thou shall not steal).

Deuteronomy 23.24-25 permits what the disciples did:

When thou comest into thy neighbour's vineyard, then thou mayest eat grapes thy fill at thine own pleasure; but thou shalt not put any in thy vessel. When thou comest into the standing corn of thy neighbour, then thou mayest pluck the ears with thine hand; but thou shalt not move a sickle unto thy neighbour's standing corn.

The disciples' behavior might have irked a farmer not bound by Jewish law. Victor Davis Hanson, The Other Greeks: The Family Farm and the Agrarian Roots of Western Civilization (New York: The Free Press, 1995), pp. 140-142, discusses farmers' reactions to trespassing and the theft of produce. The reactions included:

• Taking the thief to court. There seems to have been an old Athenian law that made grape stealing a capital offense (Alciphron 3.14; cf. Plato, Laws 844 e - 845 d; Demosthenes 47.53-56).
  
• Deterring the thief by planting prickly bushes among the crops or even placing sharp spikes to cut the feet of trespassers (scholiast on Aristophanes, Acharnians 240; Pollux, Onomasticon 1.225, 10.31; Plutarch, Moralia 94 e; Strato, Greek Anthology 12.205.4; cf. Aristophanes, Wasps 449). This measure would be more effective on a dark night than during the light of day.
  
• Chasing the trespasser or thief off (Menander, Dyscolus 109-121).

I owe all these references to Hanson and have not checked them myself yet.